LeetCode 数据库相关问题

LeetCode 数据库相关问题

select IFNULL((select distinct salary  from Employee  
order by Salary  desc  limit 1 offset 1),null) 
as 'SecondHighestSalary' from dual 

注:关于limit 和 offect的用法看下面示例

① select * from table limit 2,1;

//含义是跳过2条取出1条数据，limit后面是从第2条开始读，读取1条信息，即读取第3条数据

② select * from table limit 2 offset 1;

//含义是从第1条（不包括）数据开始取出2条数据，limit后面跟的是2条数据，offset后面是从第1条开始读取，即读取第2,3条

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    select s.Score, CAST(temp.Rank as SIGNED) as Rank from Scores s 
    left join 
    (
        select t.Score, @rank := @rank + 1 as Rank from 
        (
          select Score  from Scores group by Score order by Score desc
        ) t, (select @rank := 0) r
    ) temp on s.Score = temp.Score
    order by s.Score desc

注: @rank为临时定义一个变量rank @rank := 0 表示给变量初始化一个值